1. Field of the Invention
The present invention relates to an image display device capable of displaying different images at a plurality of viewpoints, a portable terminal equipped with the same, and a display panel and a lens incorporated in the image display device, and in particular, it relates to an image display device capable of displaying a three-dimensional image with an excellent quality, a portable terminal, a display panel, and a lens.
2. Description of the Related Art
Priorly, image display devices capable of displaying different images at a plurality of viewpoints have been investigated. As an example thereof, a three-dimensional image display device on the premise of displaying parallax images as multi-viewpoint images exists. In B.C. 280, the Greek mathematician Euclid considered that “Three-dimensional imaging is a sensation obtained when both right and left eyes simultaneously look at different images of an identical object viewed from different directions” (see authored by Chihiro Masuda, “Three-Dimensional Display,” Sangyotosho Co., Ltd., for example.) Namely, by presenting images with parallax to both right and left eyes, a three-dimensional image display device can be realized.
In order to concretely realize this function, numerous three-dimensional image display systems have been investigated so far, and these can be roughly divided into systems using eyeglasses and systems using no eyeglasses. Of these, the systems using eyeglasses include an anaglyph system, a polarizing eyeglass system utilizing polarization and the like, however, with these systems, since the burden of wearing eyeglasses cannot be essentially avoided, no-eyeglass systems using no eyeglasses have been investigated in recent years. The no-eyeglass systems include a parallax barrier system, a lenticular lens system and the like.
First, description is given of the parallax barrier system. The parallax barrier system is a three-dimensional image display system conceived by Berthier in 1896 and verified by Ives in 1903. FIG. 1 is an optical model diagram showing a method that displays three-dimensional image by a parallax barrier system. As shown in FIG. 1, a parallax barrier 105 is a barrier (shading plate) in which a large number of narrow-striped openings, namely, slits 105a have been formed. In the vicinity of one of the surfaces of this parallax barrier 105, a display panel 102 is arranged. In the display panel 102, right-eye pixels 123 and left-eye pixels 124 have been arrayed in a direction orthogonal to the longitudinal direction of the slits 105a. In addition, in the vicinity of the other surface of the parallax barrier 105, namely, on the opposite side of the display panel 102, a light source 108 is arranged.
Light emitted from the light source 108 is blocked in part by the parallax barrier 105. On the other hand, light that has passed through the slits 105a without being blocked by the parallax barrier 105 becomes light fluxes 181 through the right-eye pixels 123 or becomes light fluxes 182 through the left-eye pixels 124. At this time, the position of a viewer where recognition of a three-dimensional image becomes possible is determined based on a positional relationship between the parallax barrier 105 and pixels. Namely, it is necessary that a right eye 141 of a viewer 104 is within a passing-area of all light fluxes 181 corresponding to a plurality of right-eye pixels 123, and also, a left eye 142 of the viewer is within a passing-area of all light fluxes 182. This is a case where a middle point 143 between the viewer's right eye 141 and left eye 142 is positioned within a quadrangular three-dimensional visible area 107 shown in FIG. 1.
Of line segments extending in the array direction of the right-eye pixels 123 and left-eye pixels 124 in the three-dimensional visible area 107, a line segment that passes through an intersection point 107a between diagonal lines of the three-dimensional visible area 107 is the longest. Therefore, when the middle point 143 is positioned at the intersection point 107a, since a tolerance when the viewer's position is deviated in the left-and-right direction is maximized, this is optimal as an viewing position. Accordingly, in this three-dimensional image display method, it is recommended to the viewer to set a distance between the intersection point 107a and display panel 102 to an optimal view distance OD and view at the optimal view distance OD. Here, in the three-dimensional visible area 107, a virtual plane having the optimal view distance OD as a distance from the display panel 102 is referred to as an optimal view plane 107b. Thus, lights from the right-eye pixels 123 and left-eye pixels 124 reach the viewer's right eye 141 and left eye 142, respectively. Therefore, it becomes possible for the viewer to recognize images displayed on the display panel 102 as a three-dimensional image.
In the aforementioned parallax barrier system, since the parallax barrier had been initially arranged between the pixels and eyes when this was devised, this had obstructed the view and there had been a problem of low visibility. However, with the recent realization of liquid crystal display devices, as shown in FIG. 1, it has become possible to arrange the parallax barrier 105 behind the display panel 102, whereby the problem of visibility has been improved. Therefore, three-dimensional image display devices with the parallax barrier system have been currently actively investigated, and three-dimensional image display devices to which the parallax barrier system has been applied have been actually commercialized (see Nikkei Electronics, Jan. 6, 2003, No. 838, p. 26-27.)
For example, in Table 1 of Nikkei Electronics, Jan. 6, 2003, No. 838, p 26-27, a portable telephone equipped with a 3D-compatible liquid crystal panel has been introduced. A liquid crystal display panel of a three-dimensional image display device of this portable telephone has a 2.2-inch diagonal size and a display dot number of 176 dot wide×220 dot high. And, a liquid crystal panel for a switch to turn on/off parallax barrier effects is provided, and this can display a three-dimensional display and a planar display by switching.
Next, description will be given of the lenticular lens system. As described in the aforementioned publication, authored by Chihiro Masuda, “Three-Dimensional Display,” Sangyotosho Co., Ltd., Ives et al. invented the lenticular lens system in around 1910. FIG. 2 is a perspective view showing a lenticular lens, and FIG. 3 is an optical model diagram showing a method that displays three-dimensional image by a lenticular lens system. As shown in FIG. 2, a lenticular lens 121 has a flat plane on one of the surfaces, and on the other surface, semicylindrical convexities (cylindrical lenses 122) extending in one direction have been formed in plurality so that their longitudinal directions become mutually parallel.
And, as shown in FIG. 3, in the three-dimensional image display device by a lenticular lens system, a lenticular lens 121, a display panel 102, and a light source 108 are arranged in order from a viewer side, and on a focal plane of the lenticular lens 121, pixels of the display panel 102 are positioned. In the display panel 102, pixels 123 to display an image for a right eye 141 and pixels 124 to display an image for a left eye 142 are alternatively arrayed. At this time, groups each composed of mutually adjacent pixels 123 and 124 are corresponding to the respective cylindrical lenses (convexities) 122 of the lenticular lens 121. Thereby, when light which has been emitted from the light source 108 and has passed through the respective pixels is sorted by the cylindrical lenses 122 of the lenticular lens 121 in directions toward the right and left eyes, it becomes possible to make the right and left eyes recognize mutually different images, thus the viewer can be made to recognize a three-dimensional image.
The aforementioned parallax barrier system is a system for “blocking” an unnecessary light by a barrier, whereas the lenticular lens system is a system for changing light progressing directions, therefore, in principle, there is no decline in brightness of the display screen owing to provision of a lenticular lens. Therefore, in particular, application to portable apparatuses and the like where a high-luminance display and low-power-consumption performance are regarded as important has been considered dominant.
An example of a three-dimensional image display device developed by the lenticular lens system has been described in the aforementioned Nikkei Electronics, Jan. 6, 2003, No. 838, p. 26-27. A liquid crystal display panel of a three-dimensional image display device of this portable telephone has a 7-inch diagonal size and a display dot number of 800 dot wide×480 dot high. And, by changing the distance between the lenticular lens and liquid crystal display panel by 0.6 mm, switching between a three-dimensional display and a planar display can be made. This three-dimensional image display device has a horizontal viewpoint number of five, and five different images can be viewed by changing angles in the horizontal direction.
In addition, as an another example of an image display device capable of displaying different images at a plurality of viewpoints, a display far simultaneously displaying multiple images has been disclosed (see Japanese Published Unexamined Patent Application No. 332354/1994). The display as set forth in Japanese Published Unexamined Patent Application No. 332354/1994 simultaneously displays different planar images in each of the viewing directions by utilizing an image sorting function by a lenticular lens, whereby making it possible for a plurality of different viewers to simultaneously observe, on a single display, different planar images from different directions, respectively. FIG. 4 is a perspective view showing this display for simultaneously displaying multiple images. As shown in FIG. 4, in this display for simultaneously displaying multiple images, a lenticular lens 121 and a display panel 102 are arranged in order from a viewer 104 side. In the display panel 102, first-viewpoint pixels 125 to display an image for a first viewpoint and second-viewpoint pixels 126 to display an image for a second viewpoint are alternatively arrayed. At this time, groups each composed of mutually adjacent pixels 125 and 126 are corresponding to respective cylindrical lenses (convexities) 122 of the lenticular lens 121. Thereby, since lights from the respective pixels are sorted into different directions by the cylindrical lenses 122 of the lenticular lens 121, it becomes possible to recognize different images at different positions. By using this display for simultaneously displaying multiple images, in comparison with a case where displays for the number of people are prepared, installing space and electricity expenses and the like can be reduced. As such, currently, image display devices that can display different images at a plurality of viewpoints have been actively investigated.
However, the aforementioned prior arts have the following problems. Namely, in display panels used for image display devices, a shading portion is provided between the pixels for respective viewpoints. Since this shading portion has no display function, non-display areas where no display is carried out are formed between images for respective viewpoints. When a viewer had shifted his/her view position from images for respective viewpoints, he/she is to view non-display areas, however, since no display is carried out in the non-display areas as mentioned above, the viewer cannot view an image. Moreover, generally, it is improbable that a viewer views only at an optimal view position, and a shift in the view position can frequently occur. As a result, the viewer is conscious of a situation where viewing an image is impossible. Since no such situation occurs in an ordinal image display device having no optical components for image sorting, the viewer senses that, in an image display device which can display different images at a plurality of viewpoints, display quality is considerably deteriorated in comparison with the ordinal image display device.
Hereinafter, this problem will be described in detail by raising an example of a three-dimensional image display device by a lenticular lens system using a display panel whose pixel opening ratio in an array direction (horizontal direction) of cylindrical lenses is 50%. FIG. 5 is a plan view showing a conventional display panel whose pixel opening ratio in a horizontal direction is 50%, and FIG. 6 is an optical model diagram of a three-dimensional image display device by a lenticular lens system using the display panel shown in FIG. 5. As shown in FIG. 5, since this display panel 102 has a pixel pitch of P and a pixel opening ratio of 50% in a lens array direction (horizontal direction 112), openings 109 whose width is (P/2) are formed at the centers of pixels. Namely, a width of a shading portion 106 in the horizontal direction 112 of each pixel is (P/4). In addition, as shown in FIG. 6, in the three-dimensional image display device using this display panel 102, a lenticular lens 121, the display panel 102, and a light source 108 are arranged in order from a viewer side, and pixels of the display panel 102 are positioned at a focal plane of the lenticular lens 121. And, a distance between an apex of the lenticular lens 121 and pixels of the display panel 102 is provided as H, a refractive index of the lenticular lens 121 is provided as n, a focal distance is provided as f, and a lens pitch is provided as L. In addition, in display pixels of the display panel 102, sets of one each of left-eye pixels 124 and right-eye pixels 123 are arranged, and a pitch of each pixel is provided as P. Accordingly, a display pixel composed of one each of left-eye pixels 124 and right-eye pixels 123 has an array pitch of 2P. To this display pixel composed of two pixels of one each of left-eye pixels 124 and right-eye pixels 123, one cylindrical lens 122 is arranged in a corresponding manner.
In addition, a distance between the lenticular lens 121 and viewer is provided as an view distance OD, enlarged projection widths of pixels at this view distance OD, that is, widths of projection images of the left-eye pixel 124 and right-eye pixel 123 on a virtual plane which is distant from the lens by the view distance OD and is parallel to the lens are provided as e, respectively. Furthermore, a distance from the center of a cylindrical lens 122 positioned at the middle of the lenticular lens 121 to the center of a cylindrical lens 122 at the end of the lenticular lens 121 in the horizontal direction 112 is provided as WL, and a distance between the center of a display pixel composed of a left-eye pixel 124 and a right-eye pixel 123 positioned at the center of the display panel 102 and center of a display pixel positioned at the end of the display panel 102 in the lens array direction 112 is provided as WP. Still furthermore, incident angles and exit angles of light at a cylindrical lens 122 positioned at the middle of the lenticular lens 121 are provided as α and β, respectively, and incident angles and exit angles of light at a cylindrical lens 122 positioned at the end of the lenticular lens 121 in the lens array direction 112 are provided as γ and δ, respectively. Still furthermore, a difference between the distance WL and distance WP is provided as C, and a number of pixels contained in a area at the distance WP is provided as 2m.
Since the array pitch L of the cylindrical lenses 122 and the array pitch P of the pixels are mutually related, one is to be determined in accordance with the other, however, usually, since a lenticular lens is designed in accordance with a display panel in most cases, the array pitch P of pixels is treated as a constant. In addition, the refractive index n is determined by selecting a material of the lenticular lens 121. In contrast thereto, for the view distance OD between the lens and viewer and enlarged projection widths e of pixels in this view distance OD, desirable values are set. By use of these values, the distance H between the lens apex and pixels and the lens pitch L are determined. By Snell's law and geometric relationships, the following expressions 1 through 6 hold true.n×sin α=sin β  (Expression 1)OD×tan β=e  (Expression 2)H×tan α=P  (Expression 3)n×sin γ=sin δ  (Expression 4)H×tan γ=C  (Expression 5)OD×tan δ=WL  (Expression 6)
In addition, the following expressions 7 through 9 hold true.WP−WL=C  (Expression 7)WP=2×m×P  (Expression 8)WL=m×L  (Expression 9)
And, based on the above-described expressions 1 through 3, the following expressions 10 through 12 hold true, respectively.β=arctan(e/OD)  (Expression 10)α=arcsin(1/n×sin β)  (Expression 11)H=(P/tan α)  (Expression 12)
In addition, based on the above-described expressions 6 through 9, the following expression 13 holds true.δ=arctan(m×L/OD)  (Expression 13)
Furthermore, based on the above-described expressions 7 and 8, the following expression 14 holds true.C=2×m×P−m×L  (Expression 14)
Still furthermore, based on the above-described expression 5, the following expression 15 holds true.γ=arctan(C/H)  (Expression 15)
Here, as mentioned above, since the distance H between the lenticular lens apex and pixels is usually made equal to the focal distance f of the lenticular lens, the following expression 16 holds true, and where a radius of curvature of the lens is provided as r, the radius of curvature r is obtained by the following expression 17.f=H  (Expression 16)r=H×(n−1)/n  (Expression 17)
As shown in FIG. 6, a area where lights from all right-eye pixels 123 reach is provided as a right-eye area 171, and a area where lights from all left-eye pixels 124 reach is provided as a left-eye area 172. A viewer can recognize a three-dimensional image by positioning his/her right eye 141 at the right-eye area 171 and positioning his/her left eye 142 at the left-eye area 172. However, non-display areas 173 exist between the right-eye area 171 and left-eye area 172. For investigating the size of these non-display areas 173, where an incident angle and exit angle of a light beam which is emitted from the left end of an openings of a right-eye pixel of the display panel 102 and passes through the cylindrical lens 122 positioned at the middle of the lenticular lens 121 are provided as α1 and β1, respectively, a distance e1 from a centerline to an enlarged projection position of a centerline-side shading portion at the optimal view distance OD is obtained by the following expressions 18 through 20.n×sin α1=sin β1  (Expression 18)OD×tan β1=e1  (Expression 19)H×tan α1=P/4  (Expression 20)
Similarly, where an incident angle and exit angle of a light beam which is emitted from the right end of an opening and passes through the cylindrical lens 122 positioned at the middle of the lenticular lens 121 are provided as α2 and β2, respectively, a distance e2 from a centerline to an enlarged projection position of an end-side shading portion at the optimal view distance OD is obtained by the following expressions 21 through 23.n×sin α2=sin β2  (Expression 21)OD×tan β2=e2  (Expression 22)H×tan α2=3×P/4  (Expression 23)
As an example, where polymethyl-methacrylate (PMMA) whose refractive index n is 1.49 is used as a material of the lenticular lens 121, and a pixel pitch is provided as 0.24 mm, an optimal view distance OD is provided as 280 mm, an enlarged projection width of pixels as 65 mm, and the number m of display pixels is provided as 60, based on the aforementioned respective expressions, the distance H between the lens plane and pixels becomes 1.57 mm, the focal distance f of the lens becomes 1.57 mm, the lens pitch L becomes 0.4782 mm, and the radius of curvature r of the lens becomes 0.5161 mm. In addition, the distance e1 to an enlarged projection position of a shading portion becomes 16 mm, and e2 becomes 49 mm. These results show that, when the pixel opening ratio in the horizontal direction 112 is 50%, the width of the non-display area on the view plane also becomes 50%. Accordingly, when a viewer is positioned at the non-display area, since the viewer cannot recognize an image, he/she senses that the display quality has been considerably deteriorated.
Similar problems occur in three-dimensional image display devices not only by lens systems but also by parallax barrier systems. Hereinafter, a problem of non-display area in the parallax barrier system will be described in detail. FIG. 7 is an optical model diagram showing a three-dimensional image display device by a conventional parallax barrier system wherein a parallax barrier has been provided at a viewer's side. First, description is given of the sizes of respective portions of a three-dimensional image display device provided with a parallax barrier in which ordinal slit-like opening have been formed and a display panel. Here, for the convenience of description, a slit width of the parallax barrier is considered as being extremely small and disregardable. In addition, the slits in the parallax barrier are supposed to be arrayed in the horizontal direction in large numbers. As shown in FIG. 7, an array pitch of slits 105a in a parallax barrier 105 is provided as L, and a distance between the display panel 102 and parallax barrier 105 is provided as H. In addition, an array pitch of pixels is provided as P. As mentioned above, in the display panel 102, since display pixels are arranged as sets of two pixels, that is, one each of right-eye pixels 123 and left-eye pixels 124, an array pitch thereof becomes 2P. Since the array pitch L of the slits 105a and the array pitch P of the display pixels are mutually related, one is to be determined in accordance with the other, however, usually, since a parallax barrier is designed in accordance with a display panel in most cases, the array pitch P of pixels is treated as a constant.
In addition, a area where lights from all right-eye pixels 123 reach is provided as a right-eye area 171, and a area where lights from all left-eye pixels 124 reach is provided as a left-eye area 172. A viewer can recognize a three-dimensional image by positioning his/her right eye 141 at the right-eye area 171 and positioning his/her left eye 142 at the left-eye area 172. A distance from the display panel 102 to the viewer is provided as an optimal view distance OD. Furthermore, an enlarged projection width of one pixel on the view plane at the optimal view distance OD is provided as e.
Next, by use of the foregoing respective values, the distance H between the parallax barrier 105 and pixels of the display panel 102 is determined. By the geometric relationships shown in FIG. 7, the following expression 24 holds true, thereby, as shown in the following expression 25, the distance H is obtained.P:H=e:(OD−H)  (Expression 24)H=OD×P/(P+e)  (Expression 25)
Furthermore, where a distance between the center of a display pixel positioned at the center in a horizontal direction 112 of the display panel 102 and center of a display pixel positioned at the end in the horizontal direction 112 is provided as WP, and a distance between the centers of slits 105a corresponding to these display pixels, respectively, is provided as WL, a difference C between the distance WP and distance WL is given by the following expressions 26.WP−WL=C  (Expression 26)
In addition, in the display panel 102, where a number of pixels contained at the distance WP is provided as 2m, the following expressions 27 and 28 hold true.WP=2×m×P  (Expression 27)WL=m×L  (Expression 28)
Furthermore, since the following expression 29 holds true based on the geometric relationships, the pitch L of the slits 105a in the parallax barrier 105 is given by the following expression 30.WP:OD=WL:(OD−H)  (Expression 29)L=2×P×(OD−H)/OD  (Expression 30)
When the opening ratio of the pixels is 50%, a distance e1 from a centerline to an enlarged projection position of a centerline-side shading portion at the optimal view distance OD can be obtained by the following expression 31 using the above-described expression 24, since this is a position of a light beam emitted from the left end of an opening of the right-eye pixel 123 of the display panel 102 on an view plane at the optimal view distance OD.e1=(P/4)×(OD−H)/H  (Expression 31)
Similarly, a distance e2 from a centerline to an enlarged projection position of an end-side shading portion at the view distance OD can be obtained by the following expression 32, since this is a position of a light beam emitted from the right end of an opening of the right-eye pixel 123 of the display panel 102 on an view plane at the optimal view distance OD.e2=(3×P/4)×(OD−H)/H  (Expression 32)
Since the above-described expressions 31 and 32 indicate that when the opening ratio in the barrier array direction is 50%, the width of the non-display area on the view plane also becomes 50%. When a viewer is positioned at the non-display area, the viewer cannot recognize an image; he/she senses that display quality has been considerably deteriorated.
Furthermore, a similar problem occurs in a three-dimensional image display device provided with a parallax barrier in the rear of a display panel, as well. Hereinafter, this problem will be described in detail. FIG. 8 is an optical model diagram showing a three-dimensional image display device by a conventional parallax barrier system wherein a parallax barrier has been provided in the rear of a display panel. First, description is given of the sizes of respective portions of a three-dimensional image display device provided with a parallax barrier in which ordinal slit-like openings have been formed and a display panel. Here, for the convenience of description, a slit width of the parallax barrier is considered as being extremely small and disregardable. In addition, the slits in the parallax barrier are supposed to be arrayed in the horizontal direction in large numbers. As shown in FIG. 8, an array pitch of slits 105a in a parallax barrier 105 is provided as L, and a distance between the display panel 102 and parallax barrier 105 is provided as H, in a similar fashion as the case where the parallax barrier 105 is arranged in the front of the above-described display panel 102. In addition, an array pitch of pixels is provided as P. As mentioned above, in the display panel 102, since display pixels are arranged as sets of two pixels, that is, one each of right-eye pixels 123 and left-eye pixels 124, an array pitch thereof becomes 2P. Since the array pitch L of the slits 105a and the array pitch P of the display pixels are mutually related, one is to be determined in accordance with the other, however, usually, since a parallax barrier is designed in accordance with a display panel in most cases, the array pitch P of pixels is treated as a constant.
In addition, a area where lights from all right-eye pixels 123 reach is provided as a right-eye area 171, and a area where lights from all left-eye pixels 124 reach is provided as a left-eye area 172. A viewer can recognize a three-dimensional image by positioning his/her right eye 141 at the right-eye area 171 and positioning his/her left eye 142 at the left-eye area 172. A distance from the display panel 102 to the viewer is provided as an optimal view distance OD. Furthermore, an enlarged projection width of one pixel on the view plane at the optimal view distance OD is provided as e.
Next, by use of the foregoing respective values, the distance H between the parallax barrier 105 and pixels of the display panel 102 is determined. By the geometric relationships shown in FIG. 8, the following expression 33 holds true, thereby, as shown in the following expression 34, the distance H is obtained.P:H=e:(OD+H)  (Expression 33)H=OD×P/(e−P)  (Expression 34)
Furthermore, where a distance between the center of a display pixel positioned at the center in a horizontal direction 112 of the display panel 102 and center of a display pixel positioned at the end in the horizontal direction 112 is provided as WP, and a distance between the centers of slits 105a corresponding to these display pixels, respectively, is provided as WL, a difference C between the distance WP and distance WL is given by the following expressions 35.WL−WP=C  (Expression 35)
In addition, in the display panel 102, where a number of pixels contained at the distance WP is provided as 2m, the following expressions 36 and 37 hold true.WP=2×m×P  (Expression 36)WL=m×L  (Expression 37)
Furthermore, since the following expression 38 holds true based on the geometric relationships, the pitch L of the slits 105a in the parallax barrier 105 is given by the following expression 39.WP:OD=WL:(OD+H)  (Expression 38)L=2×P×(OD+H)/OD  (Expression 39)
When the opening ratio of the pixels is 50%, a distance e1 from a centerline to an enlarged projection position of a centerline-side shading portion at the optimal view distance OD can be obtained by the following expression 40 using the above-described expression 33, since this is a position of a light beam emitted from the left end of an opening portion of the right-eye pixel 123 of the display panel 102 on an view plane at the optimal view distance OD.e1=(P/4)×(OD+H)/H  (Expression 40)
Similarly, a distance e2 from a centerline to an enlarged projection position of an end-side shading portion at the optimal view distance OD can be obtained by the following expression 41, since this is a position of a light beam emitted from the right end of an opening of the right-eye pixel 123 of the display panel 102 on an view plane at the optimal view distance OD.e2=(3×P/4)×(OD+H)/H  (Expression 41)
Since the above-described expressions 40 and 41 indicate that when the opening ratio in the barrier array direction is 50%, the width of the non-display areas on the view plane also becomes 50%. When a viewer is positioned at the non-display area, the viewer cannot recognize an image; he/she senses that display quality has been considerably deteriorated.
Although a description has been given of a deterioration in display quality caused by a shading portion of a display panel while raising the examples of conventional three-dimensional image display devices, this problem is not limited to the three-dimensional image display devices and can similarly occur in image display devices as long as these are provided with optical components such as lenticular lenses and parallax barriers and the like.